The present invention deals with medical tubes. More particularly, the present invention deals with medical tubes, such as catheters.
Flow directed or flow assisted catheters are catheters which are used to access extremely tortuous vasculature, such as neuro vasculature. Conventional, over-the-wire catheters can also be used, but exhibit limitations in their ability to reach and maneuver within such intricate vasculature. Therefore, the flow assisted catheter is used.
Flow assisted catheters typically have a distal portion which is extremely flexible. Some flow assisted catheters also typically have an inflatable balloon or bulbous member at their distal ends. The flow assisted catheter is inserted into a vessel to be accessed through a guide catheter, and fluid may typically be pulsed through the guide catheter to carry the flow assisted catheter into the desired vessel. Once in the vessel, the flow assisted catheter is drawn through the vessel (primarily by blood flow) and is fed into the vessel by the physician. If the catheter has a balloon, the balloon is inflated to increase the drag between the blood flowing in the vessel and the distal end of the flow assisted catheter. The balloon is essentially carried by the flow through the vasculature to a target site. This draws the catheter along to the target site.
If the distal tip of the catheter becomes frictionally engaged with a vessel wall, or becomes "hung up" at a vessel branch, slack develops in the catheter. The physician then slightly withdraws the catheter until the catheter has moved away from the vessel wall or branch and is again free to move within the vessel. Once flow has taken up all the slack, the physician then feeds additional catheter length into the vessel.
In addition, some prior flow directed catheters included bent (typically steam formed) tips at the distal end of the flow directed catheter. This has been done in an effort to provide some selective tracking of the flow directed catheter into a desired vessel branch.
Current flow directed catheters suffer from a number of disadvantages. The distal portion of the flow directed catheter must be extremely flexible so that it is capable of tracking the intricate vasculature to the site to be accessed under the influence of flow in the vessel. Consequently, conventional flow directed catheters have had distal portions formed of material which is extremely flexible, and which is also quite soft. Typically, the softer the material, the lower the burst pressure. Thus, some conventional flow assisted catheters are formed with distal shaft portions with undesirably low burst pressure. This can cause the catheter to burst when injectate is introduced through the catheter.
Further, soft materials commonly have undesirably low tensile strength and also tend to stick to the vessel wall. This can cause the catheter to hang up in the vessel more often. When withdrawing the catheter to disengage it from the vessel wall, or when removing the catheter from tortuous vasculature, a catheter with such low tensile strength is susceptible to breakage.
In addition, when the physician is feeding the catheter into the vessel, the highly flexible distal portion of the conventional flow directed catheter can accumulate slack and loop. Then, when the treating physician withdraws the flow directed catheter, it can easily kink.
Further, the flexible nature of the distal portion of conventional flow directed catheters makes it virtually non-torquable by the treating physician. In other words, if the treating physician rotates or torques the proximal end of the flow directed catheter, the distal portion of the flow directed catheter is so flexible, and has such low torsional rigidity, that the torque does not transfer to the distal end. The physician must over-rotate the proximal end of the catheter, withdraw the catheter a short distance, allow the catheter to advance in the vessel and hope for some unpredictable amount of torque at its distal end. This makes selective tracking very difficult and cumbersome, even when the catheter includes a shaped tip.
The inability to transfer torque, in itself, leads to another significant problem as well. When the flow directed catheter hangs up in the vessel, the attending physician cannot break the friction between the catheter and the vessel wall by simply torquing the catheter. Rather, as described above, the physician must withdraw the flow directed catheter to some extent so it disengages from the vessel wall. Repeatedly withdrawing and advancing the flow directed catheter causes the treating physician to take an undesirable amount of time in accessing the target vasculature.
Also, in order to make the catheters highly flexible, they are often made with a very small diameter. This results in very low flow rates of injectate through the catheter and also makes it particularly difficult, if not impossible, to use such catheters to deliver large particles or coils. Finally, the soft materials used with such catheters are not typically compatible with some agents, such as alcohol. This is undesirable since a physician may wish to deliver alcohol with such a catheter.